It is often desirable to sense or detect magnetic fields such as magnetic fields generated from underground objects or within a living organism. The detection of magnetic fields may aid in geophysical mapping, underground deposit detection, navigation, and physiological mapping. For example, the detection of biomagnetic signals, in the form of weak magnetic signals, within the human body may enable the temporally and spatially resolved mapping of current dipoles within the human body. The two main biological sources of magnetic fields that have been sensed or detected are the human heart and brain. One advantage of detecting magnetic signals rather than electrical signals outside the body is that no electrodes have to be in contact with the patient's body directly. The magnetic signal may also have a richer content of information than the electrical counterpart.
Functional brain studies using magnetoencephalography (MEG) have been a growing medical research field over the past years. The spatial and temporal magnetic field distribution at different locations around the head may be detected after visual or auditory stimulation of the patient, for example. This method may allow for detection with improved signal to noise, since the signal may be averaged over many stimulation cycles.
Recently, the MEG has become a valuable tool for the clinical diagnostics in areas such as epilepsy and brain monitoring. Even though the magnetic signal may be detected in many places around the patients head, determining the position of origin of the magnetic field has remained a challenge. The placement of the electrodes or sensors and the use of mathematical algorithms have provided some estimations of the origin of the magnetic fields, but the quality of such estimations remains in question.
Many of the brain studies in the prior art have been performed with superconducting quantum interface devices (SQUIDs). SQUIDs measure the magnetic flux through a pickup coil that has to be kept at cryogenic temperatures. Maintaining these cryogenic temperatures may be complex, expensive and may require a substance (cryogen) that occurs in limited quantities on earth.
Large scale atomic magnetometers have a sensitivity comparable to the sensitivity of SQUIDs, reaching sensitivities below 1 fT√Hz. For example, large scale atomic magnetometers have shown the ability to measure magnetic fields of the human brain after auditory stimulation. This ability has been shown by placing a single large vapor cell proximate to a patient's head and selecting different “channels” by different laser beams probing different volumes within the cell. An advantage of the atomic magnetometers over SQUIDs are that no cryogenics are needed.
Large-scale atomic magnetometers, in addition to being large, expensive and difficult to operate, may have electrical conducting elements in the immediate vicinity of the sensor head in order to transmit signals and power to the sensor. Electrically conducting elements are known to cause fluctuating magnetic fields, which can disturb the magnetic environment around the sample being monitored. Additionally, electrical connections between the sensor head and the instrumentation box can cause difficulty when the sensor is operated in a high-voltage environment. Further, conventional atomic magnetometers are typically operated by driving the atoms at the sample location with an oscillating magnetic field. This oscillating field may extend into the region around the sensor head and may create interference with other sensors in the immediate vicinity or with the sample being monitored.
What is needed is an atomic magnetometer having magnetic sensors and methods for detecting magnetic fields that improve upon the deficiencies of the prior art.